The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. One type of implantable medical device that can be used is an Implantable Neuro Stimulator (INS).
An INS generates an electrical stimulation signal that is used to influence the human nervous system or organs. Electrical contacts carried on the distal end of a lead are placed at the desired stimulation site such as the spine and the proximal end of the lead is connected to the INS. The INS is then surgically implanted into an individual such as into a subcutaneous pocket in the abdomen. The INS can be powered by an internal source such as a battery or by an external source such as a radio frequency transmitter. A clinician programs the INS with a therapy using a programmer. The therapy configures parameters of the stimulation signal for the specific patient's therapy. An INS can be used to treat conditions such as pain, incontinence, movement disorders such as epilepsy and Parkinson's disease, and sleep apnea. Additional therapies appear promising to treat a variety of physiological, psychological, and emotional conditions. As the number of INS therapies has expanded, greater demands have been placed on the INS. Examples of some INSs and related components are shown and described in a brochure titled Implantable Neurostimulation Systems available from Medtronic, Inc., Minneapolis, Minn.
The effectiveness of the therapy as provided by the INS is dependent upon its capability of adjusting the electrical characteristics of the stimulation signal. For example, stimulation waveforms can be designed for selective electrical stimulation of the nervous system. Two types of selectivity may be considered. First, fiber diameter selectivity refers to the ability to activate one group of nerve fibers having a common diameter without activating nerve fibers having different diameters. Second, spatial selectivity refers to the ability to activate nerve fibers in a localized region without activating nerve fibers in neighboring regions.
The tissue around a first stimulated electrode can be damaged by a charge accumulation as a result of electrical stimulation. Thus, a recharging interval is typically utilized to balance a charge accumulation that may occur around the surrounding tissue of the first stimulated electrode. Typically an implantable medical device (such as an implantable neurological device), utilizes a passive recharge interval to balance the accumulated charge. The passive recharge interval can be increased in order to better balance the charge. However, a stimulation pulse may be delayed as a result of increasing the passive recharge interval. Moreover, a stimulation pulse may be used to pre-condition a main stimulation pulse.
The above observations may require the clinician to consider a number of factors such as the type of disorder and the specific condition of the patient in order to determine the electrical characteristics of the stimulation signal. Apparatus and method that provide flexibility in adjusting the electrical characteristics of the stimulation signal (such as an amplitude and electrical polarity of a stimulation pulse) in order to improve the effectiveness of treatment and to facilitate the clinician's task is beneficial to the field of Implantable Neuro Stimulators.